JP2006224652A - Laser exposure system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser exposure system correcting aberration in a structure at a low cost without making the structure complicated when scanned with laser light without using an fθ lens. <P>SOLUTION: The laser exposure system, which forms an image by scanning an image forming surface of paper with laser light, is provided with: an image data generating part 3 which generates image data to form an image; an acoustooptic element 21 which modulates the laser light from the generated image data; and a polygon mirror 28 which scans the surface with the modulated laser light. The image data generating part 3 is provided with an image correction means 3b which corrects aberration caused by a difference in distance between a laser light reflection position of the polygon mirror 28 and the image forming surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laser exposure apparatus that forms an image by scanning a laser beam on an image forming surface of an image forming medium.

  A configuration example of a laser exposure apparatus that forms an image on an emulsion surface of paper (corresponding to an image forming medium) will be described. As main components of the laser exposure apparatus, a laser light source, an acousto-optic element (corresponding to a light modulator), a polygon mirror (rotating polygon mirror), and an fθ lens are arranged along the optical path of the laser light.

  Image data for image formation is acquired from photographic film or storage media, and final image data is created in an image data creation unit. Laser light output from the laser light source passes through the acoustooptic device, and is modulated by the acoustooptic device based on the image data. The light-modulated laser light is reflected by a polygon mirror that rotates at high speed and deflected to paper. Thereby, the laser beam is scanned in the width direction of the paper (main scanning), and an image is printed and exposed on the emulsion surface of the paper.

  Here, the distance between the laser beam reflection position of the polygon mirror and the paper emulsion surface (image forming surface) is closest to the center of the scanning range and becomes longer toward the periphery. Since the polygon mirror rotates at an equiangular speed, the pitch between pixels (scanning speed) becomes wider (faster) toward the periphery. Therefore, in this state, since a distorted image is formed, the fθ lens is disposed between the polygon mirror and the paper. The fθ lens corrects the scanning speed of the laser beam so that the scanning speed of the laser beam on the image forming surface is constant.

  However, in the case of a laser light source device that handles laser light of a plurality of wavelengths (when forming a color image), there is a problem that color misregistration occurs because there is chromatic aberration for each wavelength. Even with an fθ lens, aberrations cannot be completely corrected, and the scanning speed in the main scanning direction cannot always be made constant. Although it is possible to manufacture an fθ lens with extremely small aberrations, there is also a problem that since the yield loss is large, the cost increases and only a small amount can be obtained.

  Therefore, apparatuses disclosed in Patent Documents 1 and 2 below are known as laser exposure apparatuses that do not use an fθ lens. These apparatuses include a mechanism for bending the paper along the scanning direction of the imaging spot of the laser beam. That is, the paper is bent in an arc shape having a radius from the reflection position by the rotary polygon mirror to the image forming surface, and the paper is conveyed.

  However, since a mechanism for bending the paper is required, there arises a problem that the configuration is complicated. In addition, in order to correct aberrations with high accuracy, it is necessary to provide accuracy for the shape to be bent, and it is difficult to transport the paper in such a state.

JP 11-149128 A JP 2001-337395 A

  The present invention has been made in view of the above circumstances, and the problem is that, when scanning laser light without using an fθ lens, laser exposure that can correct aberrations with an inexpensive configuration without complicating the configuration. Is to provide a device.

In order to solve the above problems, a laser exposure apparatus according to the present invention comprises:
A laser exposure apparatus for forming an image by scanning a laser beam on an image forming surface of an image forming medium,
An image data creation unit for creating image data for image formation;
A light modulator that modulates laser light based on the created image data;
A rotating polygon mirror for scanning the light-modulated laser light,
The image data creation unit includes image correction means for correcting aberration caused by a difference in distance from the laser light reflection position of the rotary polygon mirror to the image forming surface.

  The operation and effect of the laser exposure apparatus having this configuration will be described. The image data creation unit creates image data for image formation, and the light modulation unit optically modulates the laser beam based on the image data. Various methods for performing optical modulation are conceivable, but are not limited to specific methods. The light-modulated laser light is scanned by a rotating polygon mirror, and an operation for forming an image on the image forming surface of the image forming medium is performed.

  Here, the image data created by the image data creation unit includes image correction means for correcting aberration caused by the difference in distance from the laser beam reflection position of the rotary polygon mirror to the image forming surface. Even if it is not used, the aberration caused by the difference in scanning speed can be corrected. Further, not only the fθ lens is not used, but also mechanical correction means such as bending the image forming medium is not required. As a result, aberration can be corrected with an inexpensive configuration without complicating the configuration.

  It is preferable that the image correction means according to the present invention performs correction so that the distance between the pixels is short or overlapped by flattening the pixels toward the center of the scanning range by the laser beam.

  That is, comparing the uncorrected image data with the corrected image data, the corrected image data is in a state in which the pixels are flattened in the scanning direction toward the center, and therefore the center region spreads in the main scanning direction. Such image data is obtained. When scanning is actually performed using the corrected image data, since the scanning speed increases toward the periphery of the scanning range, the distortion is canceled and an appropriate image is formed.

The image correction means according to the present invention includes:
It is preferable to have dot clock generating means for generating a dot clock such that the frequency of the dot clock for controlling the timing of sending the pixel signal constituting the image data to the light modulator increases toward the end in the main scanning direction. .

  Normally, the frequency of the dot clock that controls the timing for sending the pixel signal to the light modulation unit is constant. That is, the pixel signals are transmitted to the light modulation unit at regular intervals, but when the fθ lens is not used, the interval between formed pixels (dots) becomes wider toward the end in the main scanning direction. Therefore, a dot clock is generated such that the frequency of the dot clock for controlling the timing of sending out the pixel signal becomes higher toward the end in the main scanning direction. Thereby, on the image forming surface, the interval between the pixels in the main scanning direction can be made equal.

  In the present invention, the image correction unit performs light amount correction so that the relative intensity of the pixel signal becomes higher as compared with the vicinity of the center as it goes to the end in the main scanning direction during laser image scanning, and the light modulation unit It is preferable to perform light modulation with image data that has undergone light amount correction.

  For example, if the dot clock frequency is changed as described above, the irradiation amount per pixel becomes lower as it goes to the end in the main scanning direction, so that the intensity of the pixel signal becomes higher than that near the center as it goes to the end. Correct the light intensity. As a result, image distortion can be corrected and light amount unevenness can be corrected without using an fθ lens.

  A preferred embodiment of a laser exposure apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a configuration of a photographic processing apparatus in which a laser exposure apparatus is used.

<Configuration of photo processing apparatus>
The photographic processing apparatus of FIG. 1 is an apparatus that obtains digital image data by scanning a frame image formed on a developed photographic film, and creates a photographic print based on the image data. Laser exposure apparatuses equipped with a laser engine for producing photographic prints are used.

  The film scanner 1 is a device that scans and reads a frame image formed on a developed photographic film. The read digital image data of the frame image is stored in the image storage unit 2. The image data creation unit 3 has a function of creating print image data for creating a photographic print. The image data creation unit 3 includes software for an operator to set various correction parameters, hardware for generating print image data based on the set correction parameters, and the like.

  The image processing means 3a has a function of performing various image processing on the image data. For example, color / density correction, red-eye correction, backlight correction, trimming, image data enlargement / reduction processing, and the like can be given. The image correction unit 3b is a function unique to the present invention, and has a function of correcting aberration based on a difference in scanning speed of laser light, as will be described later. The correction data input unit 4 has a function of inputting various correction parameters. Correction parameters by the image processing unit 3a and the image correction unit 3b are input via the correction data input unit 4. The image transfer unit 5 transfers the print image data created by the image data creation unit 3 to the laser engine 12.

  Next, the function of the printer unit that creates a photo print based on the image data will be described. The paper magazine 10 contains paper (corresponding to a photographic photosensitive material and an image forming medium) in the form of a roll. The paper is pulled out from the paper magazine 10 and conveyed along a predetermined conveyance path. The long paper drawn from the paper magazine 10 is cut into a designated print size by the paper cutter 11. The cut paper is conveyed toward the laser engine 12, and an image is printed and exposed on the emulsion surface of the paper.

  The paper on which the image (latent image) has been baked and exposed is sent to the development processing unit 13 and subjected to development processing, and then subjected to drying processing in the drying processing unit 14, and finished photo print from the paper discharge unit 15. Is discharged outside the apparatus. The laser engine 12 and the image data creation unit 3 function as a laser exposure apparatus of the present invention.

<Configuration of laser engine>
Next, the configuration of the laser exposure apparatus will be described with reference to FIG. As a laser light source 20 that outputs laser light, a red laser light source 20R, a green laser light source 20G, and a blue laser light source 20B that output RGB laser light are provided, and an optical modulation unit 21 is provided on the laser light output side. A red acoustooptic element (hereinafter abbreviated as acoustooptic element AOM) 21R, a green AOM 21G, and a blue AOM 21B are arranged, respectively. The laser light source 20 is driven by a laser driver 22 provided for each color, and the AOM 21 is driven by an AOM driver 23 (also functioning as a light modulation unit) provided for each color. Each laser light source 20 outputs laser light having a predetermined intensity. When this laser light passes through each AOM 21, laser light that is light-modulated based on image data is output. In this embodiment, the optical modulation method using the AOM 21 is described, but the present invention is not limited to this. Further, a method of directly modulating the laser light output from the laser light source 20 without using an optical modulation element such as the AOM 21 may be used. The drivers 22 and 23 are controlled by the laser control unit 24.

  The light combining unit 25 is provided with three mirrors. The first mirror 25R reflects the red laser light from the red laser light source 20R. The second mirror 25G is a dichroic mirror, transmits red laser light, reflects green laser light from the green laser light source 20G, and combines it with red laser light. The third mirror 25B is a dichroic mirror, transmits the synthesized RG laser light, reflects the blue laser light from the blue laser light source 20B, and outputs the synthesized RGB light.

  The combined laser light is reflected in a predetermined direction by the reflection mirror 26 and passes through the cylindrical lens 27. The cylindrical lens 27 is disposed to shape the beam diameter.

  The shaped laser beam is directed to the polygon mirror 28 (corresponding to a rotating polygon mirror). The polygon mirror 28 is driven to rotate at high speed in the counterclockwise direction by the polygon drive unit 29. The polygon mirror 28 is a regular polygon (hexagon in the illustrated example) and has a large number of reflecting surfaces. The number of faces is 6 in the illustrated example, but can be set as appropriate. The laser beam is scanned in a predetermined main scanning range (angle 2Θ) by causing the laser beam to enter the rotating polygon mirror 28. The scanning direction is from left to right as indicated by arrow A.

  The paper P is nipped and conveyed by the conveyance roller 30 in a direction perpendicular to the paper surface of FIG. The conveyance roller 30 includes a driving roller and a pressure roller, and is driven by a driving motor 31. The drive motor 31 is driven by the roller drive unit 32. The polygon drive unit 29 and the roller drive unit 32 are controlled by the laser control unit 24.

  While the paper P is transported in a direction perpendicular to the paper surface (corresponding to the sub-scanning direction), the laser light is repeatedly scanned along the main scanning direction, whereby an image is printed on the emulsion surface (image forming surface) of the paper P. can do. As described with reference to FIG. 1, the print image data created by the image data creation unit 3 is transferred to the laser control unit 24 via the image transfer unit 4, and each AOM 21 is controlled based on this image data. The Thereby, the light modulation of the laser beam based on the image data is performed. In the case of forming a color image, image data constituting one image is also composed of RGB image data.

  The laser engine 12 according to the present invention does not include an fθ lens. The fθ lens has a function of performing correction so that the scanning speed on the image forming surface is constant in the scanning range of the laser beam in the main scanning direction. This point will be described in detail with reference to the scanning principle diagram of laser light in FIG.

<About laser beam scanning>
In FIG. 3, the polygon mirror 28 rotates counterclockwise and has a plurality (eight) of deflection surfaces. Here, the number of faces of the polygon mirror 28 is n, and the rotation speed is fp (Hz). The direction in which the laser beam is scanned is from the left side to the right side of the figure as indicated by arrow A.

  The paper P is transported at a transport speed vp (mm / s) along the sub-scanning direction orthogonal to the main scanning direction. The range in which the laser beam is scanned is 2Θ (deg) in terms of angle. This angle is an effective scanning angle and represents the range in which the emulsion surface of the paper P is actually scanned. If the scanning angle per pixel constituting the image is θ (deg), the polygon mirror 28 is rotated at a constant angular velocity, so that θ is constant at any position in the scanning range.

Here, when the size per pixel at both ends of the scanning range is do,
[Formula 1] do = f · tan Θ−f · tan (Θ−θ)
It is represented by In Equation 1, f represents the shortest distance (focal length) between the reflection position of the laser beam on the polygon mirror 28 and the emulsion surface. If the pixel size in the middle of the scanning range is dc,
[Formula 2] dc = f · tan θ
It is represented by As can be seen from these equations, the pixel size increases toward the periphery of the scanning range. This is because the scanning speed of the laser beam on the emulsion surface increases as it goes to the periphery. Accordingly, when the fθ lens is not used, the pixel interval usually increases toward the periphery of the scanning range, resulting in a distorted image and a reduction in image quality.

Next, looking at the resolution in the sub-scanning direction,
[Formula 3] fp = (vp / 25.4) × Ds / n
The following relational expression holds. In Equation 3, 25.4 is a coefficient for converting inches and mm. Ds (dpi) represents the resolution in the sub-scanning direction. Next, when the modulation time (pixel pitch) is ta,
[Formula 4] ta = (1 / fp) × (n × 2Θ / 720)
It can be expressed as

If the modulation speed of the laser beam on the emulsion surface is tpix (sec),
[Formula 5] tpix = ta / {(L / 25.4) × Dm}
It is represented by In this equation, L represents the effective scanning width (mm) in the main scanning direction, and Dm (dpi) represents the resolution in the main scanning direction. Also,
[Formula 6] θ = 360 × trix × fp
The following relational expression holds.

  As described above, since the scanning speed is different between the center and the periphery in the scanning range, the pixel size (pixel pitch) changes. This is because the distance between the reflection position of the laser beam on the polygon mirror 28 and each point on the emulsion surface changes. In order to correct such aberration, an fθ lens is usually used. However, the aberration cannot be completely removed, and if a high-performance fθ lens is used, the cost increases. Therefore, in the present invention, the cost is reduced by not using the fθ lens, and the image data is corrected in order to solve the problem caused by not using the fθ lens, and the laser beam is based on the corrected image data. Are configured to scan.

<Correction of image data>
Next, correction (function of the image correction unit 3b) performed on image data for correcting aberration will be described with reference to FIG. In FIG. 4, the image data before correction is indicated by G1. The left and right correspond to the main scanning direction. This image data is corrected so as to be G2 so that the center pixel pitch becomes fine. As can be seen from G2, the image data becomes longer in the main scanning direction toward the center in the main scanning direction (flattened in the main scanning direction). Accordingly, the size of the image data is increased as a whole. Using the corrected image data G2, light modulation is performed and laser light scanning is performed. Since the fθ lens is not used, the scanning speed becomes slower toward the center, so that an image (print image) formed on the paper P is as shown in G3. That is, the same image as the original image can be reproduced with a photographic print.

  Since the pixel pitch is finer toward the center, many pixels are formed at the center in the photo print (a state where the pixels are short or overlap each other). Therefore, in order to ensure the minimum resolution for photographic prints, it is preferable to configure the image data so that the peripheral resolution is a predetermined level or higher. Therefore, various specifications can be determined using the above-described equations so that the peripheral resolution is, for example, 300 dpi.

  In order to perform correction by the image correction unit 3b, it is necessary to set correction parameters in advance. This correction parameter can determine each specification shown in FIG. 3, and can be calculated theoretically. Correction parameters can be set based on the calculated data. Alternatively, the correction parameter may be set by actually creating a photographic print, reading the formed print image, and determining the difference between the read image data and the original image data.

<Configuration of Second Embodiment>
In the first embodiment, the configuration in which the aberration is corrected by correcting the image data transmitted to the laser engine 12 as the image correcting unit 3b has been described. In the second embodiment, a configuration including a light amount correction circuit and a dot clock generation circuit as image correction means will be described with reference to FIGS.

  FIG. 5 shows a configuration of a control unit that controls the laser engine 12 described in FIG. Image data is stored in the image memory 40 and transferred to a light amount correction circuit (corresponding to a light amount correction means) 42 via a FIFO memory 41. Note that image data constituting one image is formed by an aggregate of a large number of pixel data (data for one pixel). The FIFO memory 41 is a small-capacity buffer memory, and is provided for adjusting the processing speed on the upper end side and the downstream side. The memory controller 47 controls the image memory 40 and the FIFO memory 41 and sequentially transfers the image data read from the image memory 40 to the FIFO memory 41. The memory controller 47 is driven by the system clock supplied from the system clock generator 48.

  The light amount correction circuit 42 corrects the pixel data so that the luminance value of the pixel signal increases toward the end in the main scanning direction. The D / A converter 46 converts the digital pixel data output from the light amount correction circuit 42 into an analog pixel signal. The pixel signal is transmitted to the AOM driver 23 described in FIG. 2 and then transmitted to the AOM 21 as a predetermined modulation signal.

  The pixel signal transmitted from the D / A converter 46 is transmitted in synchronization with the dot clock signal supplied from the variable dot clock generation circuit 43 (corresponding to dot clock generation means). Normally, the dot clock frequency is constant, but in the present invention, a variable dot clock is used such that the frequency increases toward the end in the main scanning direction. The light amount correction circuit 42 and the variable dot clock generation circuit 43 function as the image correction unit C.

  The FIFO read controller 44 controls the timing for reading image data from the FIFO memory 41. The readout timing and the pixel data correction processing in the light amount correction circuit 42 are also controlled by the variable dot clock from the variable dot clock generation circuit 43.

  The synchronization sensor 45 is a sensor for detecting a scanning start position in the main scanning direction. Specifically, the reference position of the scanning range in the main scanning direction is detected by detecting the laser beam reflected from the polygon mirror 28 at a predetermined position. When detection by the synchronization sensor 45 is performed, scanning with laser light in the main scanning direction is started in conjunction with this timing.

  FIG. 6 shows a detailed configuration of the circuit block shown in FIG. First, the configuration of the variable dot clock generation circuit 43 will be described. The reference high-speed clock generator 430 generates a high-speed dot clock that serves as a reference. The main scanning counter 431 is a counter for designating a position (address) in the main scanning direction. When the reference high-speed clock is input, the main scanning counter 431 counts up and outputs an address signal to the phase increase amount memory 432. To do. Further, when the synchronization signal from the synchronization sensor 45 is input, the count value is reset.

  The phase increase amount data 432 as shown in FIG. 7 is stored in the phase increase amount memory 432. The horizontal axis corresponds to the position in the main scanning direction, and the vertical axis corresponds to the phase increase amount. Assuming that the laser beam is scanned from left to right in FIG. 7, the count value (address) is 0 at the left end and 4096000 at the right end (the number of pixels in the main scanning direction is 4096 and falls within one pixel). When the reference high-speed clock is 1000 clocks). As can be seen from FIG. 7, data in which the phase increase amount increases toward the end in the main scanning direction is stored in the phase increase amount memory 432 in advance. Such data can be provided in the form of a look-up table (LUT). When a specific address is given, phase increase data corresponding to that address is selected and output.

  A DDS (direct digital synthesizer) is used as a method by which the variable dot clock generation circuit 43 outputs a dot clock. For this, a waveform memory in which sine waveform data is stored in advance is prepared. The waveform memory 435 is conceptually shown in FIG. As shown in FIG. 8, the horizontal axis is the phase (address), and the peak value is uniquely determined by designating the address. If addresses are selected at regular intervals (phase increment is constant), sinusoidal waveform data with a constant frequency can be output. The longer the address interval is selected (the larger the phase increase is), the more sinusoidal waveform data with higher frequency can be output.

  In the present invention, the aforementioned phase increase amount memory 432 is provided so that the phase increase amount is not constant but variable. The adder 433 outputs data obtained by adding the phase increase amount output from the phase increase amount memory 432 and the phase amount latched in the latch circuit 434, and causes the latch circuit 434 to latch the data. The data (phase amount) latched in the latch circuit 434 becomes an address signal for selecting a peak value from the waveform memory 435. A reference high-speed clock is input to the latch circuit 434, and an address signal is output to the waveform memory 435 in synchronization with this clock signal. Further, it is reset by a detection signal from the synchronization sensor 45.

  In the example of FIG. 8, the latch circuit 434 is reset at the start of main scanning, and the address (phase) is zero. When the first phase increase amount Δ1 is input from the phase increase amount memory to the adder 433, it is transmitted to the latch circuit 434 and latched, and the peak value of the waveform memory 435 at the address Δ1 is output. Next, when the phase increase amount Δ2 is input to the adder 433, it is added to Δ1 latched in the latch circuit 434, and Δ1 + Δ2 is output to the latch circuit 434 and latched, and the waveform memory 435 at the address Δ1 + Δ2 is stored. The peak value is output. Next, when the phase increase amount Δ3 is input to the adder 433, it is added to Δ1 + Δ2 latched in the latch circuit 434, Δ1 + Δ2 + Δ3 is output to the latch circuit 434 and latched, and the peak value at the address Δ1 + Δ2 + Δ3 is output. Is done. Thereafter, the same calculation is repeated each time the main scanning counter 431 counts up, and the waveform data is output from the waveform memory 435.

  FIG. 8 shows the concept of controlling one clock in the laser main scanning direction. Here, the clock can be distorted by gradually decreasing Δ1, Δ2, Δ3... By changing this distortion, the time width of one clock can be changed. In other words, when viewed as a whole in the main scanning direction, the dot clock width is controlled differently, and the width is large in the middle of the main scanning and decreases toward the end.

  The output waveform data 435 is a stepped digital waveform, which is once converted into an analog waveform by the D / A converter 436. Next, it is shaped into a sine waveform from which the stepped portion has been removed by passing through a low-pass filter 437. By comparing this sine waveform with a reference voltage by the comparator 438, it is converted into a rectangular wave, and a dot clock signal is generated. This dot clock signal is not a constant frequency, but is a variable dot clock whose frequency increases toward the end in the main scanning direction.

  Next, the light amount correction circuit 42 will be described. The main scanning counter 420 is a counter having the same function as the main scanning counter 431 of the variable dot clock generation circuit 43, and is a counter for designating a position (address) in the main scanning direction. When the dot clock is input, the count is incremented and an address signal is output to the light quantity correction value memory 421. The relationship between the position (address) in the main scanning direction and the light amount correction value is as shown in FIG. 7, and the pixel data is corrected so that the luminance increases toward the end in the main scanning direction. The light quantity correction value can also be provided in the form of a lookup table. When a certain address is designated, the light quantity correction value corresponding to that address is selected and output.

  The multiplier 422 outputs the result of multiplying the pixel data transmitted from the FIFO memory 41 and the light amount correction value, and outputs the result to the D / A converter 46. The data is transmitted from the D / A converter 46 to the AOM driver 23. The pixel signal output from the D / A converter 46 is transmitted at the timing of the variable dot clock supplied from the variable dot clock generation circuit 43. In addition, the pixel signal is light quantity corrected, and an image free from distortion and light quantity unevenness is formed on the paper.

  The phase increase amount stored in the phase increase amount memory 432 and the light amount correction value stored in the light amount correction value memory 421 are based on design values such as the shape and rotation speed of the polygon mirror 28 and the distance from the paper exposure surface. Since it can be calculated theoretically, the calculated value can be input.

<Another embodiment>
The configuration of the laser engine in the present embodiment shows an example, and is not limited to this. As the laser light source, an appropriate system such as a semiconductor laser or an LD excitation solid laser can be used. The configuration of the optical path can be changed as appropriate.

  Between the polygon mirror 28 and the paper P, a cylindrical lens for beam shaping or the like may be arranged. The paper used may be a medium other than a photographic material having an emulsion surface.

Schematic diagram showing the configuration of the photo processing device Schematic diagram showing the configuration of the laser exposure apparatus Diagram explaining scanning of laser beam by polygon mirror The figure explaining the function of an image correction means Circuit block diagram showing the configuration of the second embodiment of the image correction means The figure which shows the detailed structure of the circuit block shown in FIG. The figure which shows the contents of the data of the phase increase amount and the light quantity correction value The figure explaining the operation which outputs the sine waveform from the waveform memory

Explanation of symbols

3 Image data creation unit 3a Image processing unit 3b Image correction unit 4 Image data input unit 5 Image transfer unit 12 Laser engine 20 Laser light source 21 Acoustooptic device (AOM)
22 Laser driver 23 Polygon driver 24 Laser control unit 28 Polygon mirror 29 Polygon drive unit 42 Light amount correction circuit 43 Variable dot clock generation circuit 44 FIFO read controller 45 Synchronization sensor 46 D / A converter 420 Main scanning counter 421 Light amount correction value memory 422 Multiplication 431 Main scanning counter 432 Phase increment memory 433 Adder 435 Waveform memory P Paper

Claims (4)

A laser exposure apparatus for forming an image by scanning a laser beam on an image forming surface of an image forming medium,
An image data creation unit for creating image data for image formation;
A light modulator that modulates laser light based on the created image data;
A rotating polygon mirror for scanning the light-modulated laser light,
The laser exposure apparatus, wherein the image data creation unit includes an image correction unit that corrects an aberration caused by a difference in distance from a laser beam reflection position of the rotary polygon mirror to an image forming surface.   2. The laser exposure apparatus according to claim 1, wherein the image correction unit performs correction so that a distance between pixels is shortened or overlapped by flattening a pixel toward a center of a scanning range by a laser beam. The image correcting means includes
It has dot clock generation means for generating a dot clock such that the frequency of the dot clock for controlling the timing of sending the pixel signals constituting the image data to the light modulator becomes higher toward the end in the main scanning direction. The laser exposure apparatus according to claim 1 or 2.   The image correction unit performs light amount correction so that the relative intensity of the pixel signal becomes higher as it goes to the end in the main scanning direction in laser image scanning, and the light modulation unit performs light amount correction. The laser exposure apparatus according to any one of claims 1 to 3, wherein light modulation is performed by the image data made.

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